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Fair Value Measurements - Rating of U.S. Corporate Debt Securities (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments $ 80 $ 188
U.S. corporate debt securities [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   57 [1]
U.S. corporate debt securities [Member] | AAA to AA [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   26
U.S. corporate debt securities [Member] | A+ to A- [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   25
U.S. corporate debt securities [Member] | BBB+ to Unrated [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   6
U.S. corporate debt securities [Member] | Level 2 | AAA to AA [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   26
U.S. corporate debt securities [Member] | Level 2 | A+ to A- [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   25
U.S. corporate debt securities [Member] | Level 2 | BBB+ to Unrated [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   6
U.S. corporate debt securities [Member] | Level 3 | AAA to AA [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   0
U.S. corporate debt securities [Member] | Level 3 | A+ to A- [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   0
U.S. corporate debt securities [Member] | Level 3 | BBB+ to Unrated [Member]
   
Rating Of Available For Sale Securities [Line Items]    
Available-for-sale investments   $ 0
[1] The majority of our U.S. corporate debt securities represented investments in the financial services, consumer products and insurance sectors at December 31, 2011.